The present invention relates, in general, to a bumper of a motor vehicle.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Bumpers are typically arranged across the front and rear of a motor vehicle between the plastic shell of the vehicle body and the frame of the motor vehicle. To prevent damage to the vehicle body structure in the event of a crash or impact at low speed, crash boxes are integrated to absorb energy caused by the impact and to convert the energy in deformation work. Also, pedestrians are protected by bumpers in the event of an impact by a motor vehicle.
Bumpers typically include a rigid cross member arranged in the horizontal plane in perpendicular relationship to the travel direction and attached to the right and left side rails via crash boxes, respectively. The crash boxes absorb the impact energy by undergoing a plastic deformation in the event of a frontal crash at low speed, typically in a rear-end collision on urban streets. Official regulations as well as voluntary intents by the automobile industry to protect passengers led to the construction of bumpers to also minimize stress to a pedestrian's lower extremities in the event of a collision between the pedestrian and the vehicle front. For that purpose, impact tests have been established using a leg impactor to ensure compliance with several limit values.
Oftentimes, to provide adequate protection of pedestrians, bumpers are provided with energy absorbers attached directly to the front side of the cross member. An example is disclosed in German Pat. No. DE 44 13 641 C1, in which the use of shock absorbers are described which are made of plastic foam or a plastic honeycomb structure. Other examples involve the use of an undulating leaf spring as energy absorbing element (U.S. Pat. No. 4,542,925), or energy absorbers in the form of thin sheet metal strips which are attached as open profile onto the cross member.
An alternative to the afore-described passive systems involves the construction of bumpers with actively controllable elements to react to an impact. An example is disclosed in U.S. Pat. No. 6,174,008 and involves a bumper which is mounted in such a way that it can be moved between a rest position and an operating position. The movement is hereby realized by a shape-memory spring which acts on the bumper and is prestressed in the rest position.
It would be desirable and advantageous to provide an improved bumper to obviate prior art shortcomings and to exhibit superior impact absorption characteristics while still being simple in structure so as to, i.a. reduce a vehicle overhang.